The present invention relates to a transparent conductive heat sealing material suitably applicable for a lid of a carrier tape package used upon storing, transporting or mounting electronic products easily susceptible to breakage by static electricity, particularly such as a chip-type electronic product or an electronic circuit board already mounting parts, and a carrier tape lid using the same.
Surface-mounted chip-type electronic parts such as ICs as well as transistor, diodes, capacitors and piezo-electric element registers are supplied in the form packaged in a carrier tape package comprising a plastic carrier tape (hereinafter simply referred to as a xe2x80x9ccarrier tapexe2x80x9d) having continuously emboss-formed pockets capable of housing the parts in response to shapes of the parts and a carrier tape lid (hereinafter sometimes simply referred to as a xe2x80x9clidxe2x80x9d) heat-sealed to the carrier tape. The electronic parts therein contained are automatically taken out from the carrier tape after peeling off the lid of the carrier tape package, and surface-mounted on an electronic circuit board.
Along with the recent remarkable improvements achieved in the surface-mounting technology, these electronic parts transported or otherwise handled in the above-mentioned carrier tape package have improved performance and are downsized. These electronic parts may be broken under the effect of electrostatic discharge as a result of contact between the carrier tape emboss inner surface or the lid inner surface and the electronic parts caused by vibration during transportation of the carrier tape package. A similar trouble may occur from static electricity produced upon peeling off the lid from the carrier tape. Measures against electrostatic troubles have therefore been the most important problem to be solved in the carrier tape and the lid.
A charge preventing treatment (an antistatic treatment) of a carrier tape has conventionally been accomplished through kneading of carbon black into a material used, or coating, giving satisfactory effects. For the lid, however, transparency to an extent permitting visual recognition of the contents is required. Since an antistatic treatment similar to that for the carrier tape cannot be conducted, therefore, the following antistatic treatments have been proposed:
(1) Kneading a surfactant-based antistatic agent into plastics, or conducting coating onto a plastic surface;
(2) Laminating aluminum foil films;
(3) Coating a plastic resin prepared by kneading a metal oxide-based conductivity agent such as tin oxide.
The method (1) above has, however, a problem in that the antistatic function deteriorates or even disappears under a low-humidity condition. The methods (2) and (3) above have a problem in that transparency of the lid cannot be maintained, and visual recognition of the contents is difficult or even impossible.
The present invention was developed to solve the aforementioned problems, and has a main object to provide a transparent conductive heat sealing material of which the antistatic function is not deteriorated even at low humidity, and which has a transparency to an extent permitting visual recognition of contents, and a carrier tape lid using the same.
The invention provided a transparent conductive heat sealing material comprising conductive fine particles 50% of which have a particle size of up to 1.0 xcexcm at least dispersed in a heat sealable synthetic resin.
The transparent conductive heat sealing material of the invention is a heat sealing material which is a conductive and excellent in transparency because conductive fine particles 50% of which have a particle size of up to 1.0 xcexcm dispersed in a heat-sealable synthetic resin.
In the invention, the transparent conductive heat sealing material should preferably have a surface resistance of 104 to 1012 xcexa9/square. The transparent conductive heat sealing material should preferably have optical properties resulting in a full-light transmissivity of at least 70% in a laminated member obtained by laminating the transparent conductive heat sealing material with other lamination material, and in a haze of up to 25%. When the transparent conductive heat sealing material of the invention is used as a heat sealing material in a carrier tape lid which is the most suitable use for a laminated member obtained by laminating the transparent conductive heat sealing material layers of the invention, the required antistatic property and optical properties are within the above-mentioned ranges.
In the invention, the aforementioned conductive fine particles should preferably be acicular fine particles. If the fine particles are acicular in shape, the individual fine particles dispersed in a heat-sealable synthetic resin would highly probably be kept in contact between them, so that a small quantity of such fine particles can bring about an effect of reducing electric resistance. The material, being satisfactory in transparency, is favorable for improving antistatic effect while maintaining satisfactory transparency.
The above-mentioned conductive fine particles should preferably comprise fine particles prepared by imparting conductivity to a metal oxide. Among others, the fine particles prepared by imparting conductivity to the metal oxide should preferably comprise acicular powder of antimony-doped tin oxide. When availability of particles and performance are taken into account, the acicular powder of conductive fine particles should preferably comprise fine particles prepared by imparting conductivity to a metal oxide, and among others, acicular powder of antimony-doped tin oxide.
In an aspect of the invention, the above-mentioned conductive fine particles may comprise spherical fine particles. Spherical fine particles also have an effect of reducing electric resistance. Because of a satisfactory transparency, such fine particles are preferable for improving antistatic effect while maintaining satisfactory transparency.
In this case, the conductive fine particles should preferably comprise fine particles prepared by imparting conductivity to a metal oxide, and among others, the fine particles prepared by imparting conductivity to the metal oxide should preferably comprise spherical powder of antimony-doped tin oxide.
In an aspect of the invention, the heat-sealable synthetic resin should preferably comprise any one of a polyester resin, a polyurethane resin, a vinyl chloride-vinyl acetate copolymer resin, an acryl resin, and an ethylene-vinyl acetate copolymer resin, or a combination thereof.
The invention provides, furthermore, a carrier tape lid formed by a transparent conductive heat sealing material comprising conductive fine particles 50% of which have a particle size of up to 1.0 xcexcm at least dispersed in a heat sealable synthetic resin, and comprising at least a heat sealing layer heat-sealed by a carrier tape, an outer layer formed by a biaxially oriented film, and a cushion layer arranged between the heat sealing layer and the outer layer.
The carrier tape lid of the invention has a heat sealing layer formed with the above-mentioned transparent conductive heat sealing material. When heat-sealing it to a carrier tape, it brings about an effect of permitting visual recognition of the contents while keeping a satisfactory antistatic function.
In this case, the cushion layer should preferably comprise a layer mainly comprising a polymer material having a low degree of crystallinity. By using a polymer material having a low crystallinity as a main constituent, it is possible to inhibit contraction of the cushion layer during the manufacturing process of the carrier tape lid. It is thus possible to prevent curling of the carrier tape lid caused by contraction of the cushion layer, giving a better operability.
In the carrier tape lid of the invention, the cushion layer may comprise a layer formed by polyolefin having a density within a range of from 0.900 to 0.910 g/cm3 and a weight average molecular weight within a range of from 20,000 to 100,000. Selection of this material as a cushion layer improves cushioning function, thus permitting reduction of the thickness of the cushion layer. By thus reducing the thickness of the cushion layer, it is possible to inhibit contraction of the cushion layer during manufacture, prevent curling of the resultant carrier tape lid, and improve operability.
Furthermore, the cushion layer may comprise at least three kinds of resin including at least an ethylene-xcex1-olefin copolymer and a styrene-butadiene block copolymer, selected from the group consisting of ethylene-xcex1-olefin copolymer having a density within a range of from 0.915 to 0.940 g/cm3, a styrene-butadiene copolymer comprising from 50 to 90 wt. % styrene and from 50 to 10 wt. % butadiene, a hydrogenated styrene-butadiene block copolymer comprising from 10 to 50 wt. % styrene and from 90 to 50 wt. % butadiene, and a high-impact polystyrene.
The above-mentioned cushion layer may also have a double-layer structure comprising a first resin layer and a second resin layer in contact with the heat sealing layer; the first resin layer comprises an ethylene-xcex1-olefin copolymer having a density within a range of from 0.915 to 0.940 g/cm3; and the second resin layer comprises a resin composition prepared by adding from 5 to 30 weight parts hydrogenated styrene-butadiene block copolymer comprising from 10 to 50 wt. % styrene and from 90 to 50 wt. % butadiene to 100 weight parts resin composition comprising from 10 to 90 wt. % ethylene-xcex1-olefin copolymer having a density within a range of from 0.915 to 0.940 g/cm3 and from 70 to 30 wt. % styrene-butadiene block copolymer comprising from 50 to 90 wt. % styrene and from 50 to 10 wt. % butadiene.
The above-mentioned cushion layer may have a triple-layer structure comprising a first resin layer, a second resin layer and a third resin layer in contact with the heat sealing layer; the first resin layer comprises an ethylene-xcex1-olefin copolymer having a density within a range of from 0.915 to 0.940 g/cm3; the second resin layer comprises a resin composition containing from 10 to 90 wt. % ethylene-xcex1-olefin copolymer having a density within a range of from 0.915 to 0.940 g/cm3, and from 70 to 30 wt. % styrene-butadiene block copolymer containing from 50 to 90 wt. % styrene and from 50 to 10 wt. % butadiene; and the third resin layer comprises a resin composition prepared by adding from 5 to 30 weight parts hydrogenated styrene-butadiene block copolymer containing from 10 to 50 wt. % styrene and from 90 to 50 wt. % butadiene to 100 weight parts resin composition comprising from 10 to 90 wt. % ethylene-xcex1-olefin copolymer having a density within a range of from 0.915 to 0.940 g/cm3 and from 70 to 30 wt. % styrene-butadiene block copolymer containing from 50 to 90 wt. % styrene and from 50 to 10 wt. % butadiene.
The invention also provides a carrier tape lid formed by a transparent conductive heat sealing material comprising conductive fine particles of which 50% have a particle size of up to 1.0 xcexcm, and comprising at least a heat sealing layer heat-sealed by a carrier tape, an outer layer formed by a biaxially oriented film, a cushion layer arranged between the heat sealing layer and the outer layer, and a primer layer arranged between the heat sealing layer and the cushion layer.
Because, in the carrier tape lid of the invention, a primer layer is further arranged between the heat sealing layer and the cushion layer of the carrier tape lid, it is suitably applicable particularly to a case where it is required to inhibit delamination between the cushion layer and the heat sealing layer, or to a case where it is required to improve adhesivity between the cushion layer and the heat sealing layer. Delamination between the cushion layer and the heat sealing layer is therefore inhibited, thus enabling to improve exterior view upon peeling off the lid heat-sealed to the carrier tape. Since it is possible to improve adhesivity between the cushion layer and the heat sealing layer, it is possible to adjust adhesivity of the lid to above an appropriate level of strength.
The above-mentioned primer layer should preferably be formed by a resin composition comprising from 0 to 100 wt. % styrene-ethylene-butylene-styrene copolymer and from 100 to 0 wt. % acid-modified styrene-ethylene-butylene-styrene copolymer. According to this aspect of the invention, it is possible to remarkably improve adhesivity between the primer layer and the cushion layer, and simultaneously, to improve adhesivity also between the primer layer and the heat sealing layer. As a result, by the presence of the primer layer in between, in the heat sealing lamination of the invention, it is possible to bond the cushion layer and the heat sealing layer with a sufficient strength.
Acrylic rubber should preferably be added at a ratio of up to 60 wt. % relative to the total resin composition to the resin composition forming the primer layer. According to this aspect of the invention, it is possible to ensure more remarkable effect of the primer layer and further improve adhesivity by adding an acrylic rubber in an amount of up to 60 wt. % relative to the entire resin composition.
The invention provides furthermore a carrier tape package comprising the carrier tape lid heat-sealed to a carrier tape having continuous housing sections which house package members. The carrier tape package of the invention, having the carrier tape lid as described above, provides an effect of permitting visual recognition of the contents without causing breakage by electrostatic discharge to the packaged contents.